Geared turbofan with integral front support and carrier

ABSTRACT

A gas turbine engine includes a nacelle, and a bypass flow path in a bypass duct within the nacelle of the turbofan engine. A fan section includes a fan with fan blades. The fan section drives air along the bypass flow path. A fan shaft drives a fan that has fan blades and the fan rotates about a central longitudinal axis of the turbofan engine. A speed reduction device includes an epicyclic gear system. A turbine section is connected to the fan section through the speed reduction device and the turbine section rotates about the central longitudinal axis. A first fan bearing for supporting rotation of the fan hub is located axially forward of the speed reduction device. A second fan bearing for supporting rotation of the fan hub is located axially aft of the speed reduction device. A first outer race of the first fan bearing is fixed relative to the fan hub.

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure is a continuation of U.S. application Ser. No. 14/633,244 filed on Feb. 27, 2015, which claims priority to U.S. Provisional Application No. 61/949,331, which was filed on Mar. 7, 2014 and is incorporated herein by reference.

BACKGROUND

A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-energy exhaust gas flow. The high-energy exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section typically includes low and high pressure compressors, and the turbine section includes low and high pressure turbines.

A speed reduction device such as an epicyclical gear assembly may be utilized to drive the fan section such that the fan section may rotate at a speed different than the turbine section so as to increase the overall propulsive efficiency of the engine. In such engine architectures, a shaft driven by one of the turbine sections provides an input to the epicyclical gear assembly that drives the fan section at a reduced speed such that both the turbine section and the fan section can rotate at closer to optimal speeds.

The epicyclical gear assembly includes bearings that support rotation of gears. Loads incurred during operation can disrupt a desired relative alignment between gears and therefore the gear assembly may be supported on structures designed to accommodate such loads.

Although geared architectures improve propulsive efficiency, they present different challenges that can reduce any efficiency gains. Accordingly, turbine engine manufacturers continue to seek further improvements to engine performance including improvements to thermal, transfer and propulsive efficiencies.

SUMMARY

In one exemplary embodiment, a gas turbine engine includes a nacelle, and a bypass flow path in a bypass duct within the nacelle of the turbofan engine. A fan section includes a fan with fan blades. The fan section drives air along the bypass flow path. A fan shaft drives a fan that has fan blades and the fan rotates about a central longitudinal axis of the turbofan engine. A speed reduction device includes an epicyclic gear system. A turbine section is connected to the fan section through the speed reduction device and the turbine section rotates about the central longitudinal axis. A first fan bearing for supporting rotation of the fan hub is located axially forward of the speed reduction device. A second fan bearing for supporting rotation of the fan hub is located axially aft of the speed reduction device. A first outer race of the first fan bearing is fixed relative to the fan hub.

In a further embodiment of any of the above, the second fan bearing includes an outer race. The outer race of the first fan bearing and the outer race of the second fan bearing are fixed relative to the fan hub and rotate with the fan hub in the same direction.

In a further embodiment of any of the above, an inner race of the first fan bearing is fixed from rotation relative to an engine static structure. An inner race of the second fan bearing is fixed from rotation relative to the engine static structure.

In a further embodiment of any of the above, the epicyclic gear system includes a sun gear, star gears, a ring gear mechanically attached to the fan section, and a carrier. The carrier is fixed from rotation relative to the engine static structure.

In a further embodiment of any of the above, the first fan bearing and the second fan bearing include at least one of roller bearings, ball bearings, or tapered bearings. Each of the star gears include a star gear bearing.

In a further embodiment of any of the above, the carrier includes multiple flexible posts for mounting each of the star gears and the star gear bearing.

In a further embodiment of any of the above, the first fan bearing is at least partially axially aligned with a fan blade of the fan section.

In a further embodiment of any of the above, a carrier is fixed from rotation relative to an engine static structure without a static flexible mount.

In a further embodiment of any of the above, an inner race of the first fan bearing is fixed from rotation relative to a carrier. The carrier is fixed from rotation relative to an engine static structure.

In a further embodiment of any of the above, a high pressure compressor with a compression ratio of at least 20:1 and a fan bypass ratio greater than 10.

In a further embodiment of any of the above, a compressor section is configured to rotate with the fan section. The compressor section includes a five stage low pressure compressor with a compression ratio of at least 2:1.

In a further embodiment of any of the above, a rotating compartment wall is configured to rotate with the compressor section and form a seal with an engine static structure.

In a further embodiment of any of the above, the speed reduction device is located radially inward from a first compressor. The speed reduction device is axially aligned with the first compressor.

In another exemplary embodiment, a fan drive gear module includes a sun gear and a multitude of intermediate gears surrounding the sun gear. A carrier supports the multitude of intermediate gears. The carrier is configured to support a fan hub with a first fan bearing located on a first side of the carrier and a second fan bearing located on a second opposite side of the carrier. The carrier is configured to be fixed from rotation relative to an engine static structure without a static flexible mount. An outer race of the first fan bearing and an outer race of the second fan bearing are fixed relative to the fan hub and rotate with the fan hub in the same direction.

In a further embodiment of any of the above, an inner race of the first fan bearing is fixed from rotation relative to a carrier. The carrier is fixed from rotation relative to the engine static structure.

In a further embodiment of any of the above, each of the multitude of intermediate gears include an intermediate gear bearing. The carrier includes multiple flexible posts for mounting each of the multitude of intermediate gears and the intermediate gear bearing.

In a further embodiment of any of the above, a ring gear is fixed relative to the fan hub and the first fan bearing and the second fan bearing include at least one of roller bearings, ball bearings, or tapered bearings.

In another exemplary embodiment, a method of designing a gas turbine engine includes coupling a speed reduction device between a fan hub and a low pressure turbine drive shaft. A first fan bearing is positioned axially forward of the speed reduction device. An outer race of the first fan bearing is fixed relative to the fan hub and rotates with the fan hub relative to an engine static structure. A second fan bearing is positioned axially aft of the speed reduction device. An outer race of the second fan bearing is fixed relative to the fan hub and rotates in the same rotational direction as the outer race of the first fan bearing.

In a further embodiment of any of the above, an inner race of the first fan bearing and an inner race of the second fan bearing is positioned fixed to a carrier and fixed from rotation relative to the engine static structure.

In a further embodiment of any of the above, a ring gear of the speed reduction device relative to the fan hub is fixed to allow the ring gear to rotate with the fan hub. The first fan bearing and the second fan bearing include at least one of roller bearings, ball bearings, or tapered bearings.

The various features and advantages of this disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an example gas turbine engine.

FIG. 2 is a schematic view of an example geared architecture.

FIG. 3 is a schematic view of another example geared architecture.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gas turbine engine 20 is disclosed herein as a two-spool turbofan that generally incorporates a fan section 22, a compressor section 24, a combustor section 26 and a turbine section 28. Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section 22 drives air along a bypass flow path B in a bypass duct defined within a nacelle 15, while the compressor section 24 drives air along a core flow path C for compression and communication into the combustor section 26 then expansion through the turbine section 28. Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis A relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems 38 at various locations may alternatively or additionally be provided, and the location of bearing systems 38 may be varied as appropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 that interconnects a fan 42, a first (or low) pressure compressor 44 and a first (or low) pressure turbine 46. The inner shaft 40 is connected to the fan 42 through a speed change mechanism, which in exemplary gas turbine engine 20 is illustrated as a geared architecture 48 to drive the fan 42 at a lower speed than the low speed spool 30. The high speed spool 32 includes an outer shaft 50 that interconnects a second (or high) pressure compressor 52 and a second (or high) pressure turbine 54. A combustor 56 is arranged in exemplary gas turbine 20 between the high pressure compressor 52 and the high pressure turbine 54. A mid-turbine frame 57 of the engine static structure 36 is arranged generally between the high pressure turbine 54 and the low pressure turbine 46. The mid-turbine frame 57 further supports bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via bearing systems 38 about the engine central longitudinal axis A which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 with a compression ratio of at least 2:1 then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, then expanded over the high pressure turbine 54 and low pressure turbine 46. The mid-turbine frame 57 includes airfoils 59 which are in the core airflow path C. The turbines 46, 54 rotationally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion. It will be appreciated that each of the positions of the fan section 22, compressor section 24, combustor section 26, turbine section 28, and fan drive gear system 48 may be varied. For example, gear system 48 may be located aft of combustor section 26 or even aft of turbine section 28, and fan section 22 may be positioned forward or aft of the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. In a further example, the engine 20 bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture 48 is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine 46 has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine 20 bypass ratio is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor 44, and the low pressure turbine 46 has a pressure ratio that is greater than about five 5:1. Low pressure turbine 46 pressure ratio is pressure measured prior to inlet of low pressure turbine 46 as related to the pressure at the outlet of the low pressure turbine 46 prior to an exhaust nozzle. The geared architecture 48 may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans.

A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section 22 of the engine 20 is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft (10,668 meters), with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (′TSFC)”—is the industry standard parameter of 1 bm of fuel being burned divided by 1 bf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane (“FEGV”) system. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7° R)]^(0.5). The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second (350.5 meters/second).

FIG. 2 illustrates the inner shaft 40 driving the geared architecture 48 to turn the fan 42 and the low pressure compressor 44 together at the same rotational speed. The inner shaft 40 is connected with a sun gear 60 in the geared architecture 48. The sun gear 60 is surrounded by star gears 62 mounted on star gear bearing assemblies 64 attached to a static carrier 66. The static carrier 66 allows the star gears 62 to rotate around an axis of each star gear 62 but not around and engine axis A. The static carrier 66 is fixed relative to the engine static structure 36 on the gas turbine engine 20.

The geared architecture 48 is located radially inward and axially aligned with the low pressure compressor 44 to shorten the overall length of the gas turbine engine 20.

A fan hub 68 is supported by a forward fan bearing 70 and an aft fan bearing 72. The forward fan bearing 70 includes an inner race 74 fixed to the static carrier 66 and an outer race 76 fixed to the fan hub 68. The forward fan bearing 70 supports radial and thrust loads from a forward end of the fan hub 68.

The aft fan bearing 72 includes an inner race 78 attached to the static carrier 66, which is connected with the engine static structure 36, and an outer race 80 is attached to a rotating aft support 82. The aft fan bearing 72 supports an aft end of the fan hub 68 and carries radial loads from the fan 42.

A rotatable ring gear 84 turns the fan hub 68 and the low pressure compressor 44 at the same rotational speed. A rotating compartment wall 86 extends from the rotating aft support 82 and is sealed against the engine static structure 36 with an oil seal 88.

Scavenged oil passes through holes 90 extending through the ring gear 84, the rotating aft support 82, and the engine static structure 36 to direct oil towards the forward and aft fan bearing 70 and 72 and the geared architecture 48. A rotating cover 92 aids in retaining and directing the oil towards the forward fan bearing 70, the aft fan bearing 72, and the geared architecture 48 and to prevent the need for carbon seals.

FIG. 3 illustrates another example geared architecture 148. The geared architecture 148 is similar to the geared architecture 48 shown in FIG. 2 except where shown in FIG. 3 or described below.

A static carrier 110 includes an oil baffle 100 extending from a forward end and a cylindrical support 102 for supporting the forward fan bearing 70. An oil feed tube 106 supplies oil to the static carrier 110 and the rest of geared architecture 148. A multitude of flexible shafts 112 extend from the static carrier 110 to support the star gears 62 and the respective star gear bearing assemblies 64. The flexibility of the shafts 112 support torsional loads from the star gears 62 and star gear bearing assemblies 64 and allow the star gears 62 to be isolated from the engine static structure 36 such that a static flexible mount is not necessary to mount the geared architecture 148.

The forward fan bearing 70 in this example includes a roller bearing with the inner race 74 mounted to the cylindrical support 102 and the outer race 76 rotatably attached to the fan hub 68 through a hub support 104. Although a roller bearing is illustrated in this example for the forward fan bearing 70, a ball bearing or a tapered bearing could also be utilized.

The aft fan bearing 72, such as a ball bearing, is mounted on an aft side of the geared architecture 148 opposite from the forward bearing 70. Although a ball bearing is illustrated in this example for the aft fan bearing 72, a roller bearing or a tapered bearing could also be utilized.

The forward fan bearing 70 and the aft fan bearing 72 straddle the geared architecture 148 to greatly reduce misalignment imparted on the geared architecture 148. This eliminates the need for a flexible coupling on the geared architecture 148 to combat misalignment forces acting on the gears.

An inner shaft bearing 114 attached to the engine static structure 36 supports a forward end of the inner shaft 40 and carries both radial and thrust loads. Since the fan 42 imparts a forward thrust load and low pressure turbine 46 imparts an aft thrust load on the inner shaft 40, the opposing loads are generally cancelled out by the aft fan bearing 72 and the inner shaft bearing 114 both being attached to the engine static structure 36.

The gas turbine engine 20 is designed by attaching the geared architecture 48 or 148 device to the fan hub 68 and the inner shaft 40. The forward fan bearing 70 is positioned forward of the geared architecture 48 or 148 with the first outer race 76 connected to the fan hub 68. The aft fan bearing 72 is positioned aft of the geared architecture 48 or 148. The inner race 74 and the inner race 78 are attached to the static carrier (66 or 110). The ring gear 85 from the geared architecture 48 or 148 is connected to the fan hub 68.

The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims. 

What is claimed is:
 1. A gas turbine engine comprising: a fan section including a fan having fan blades, wherein said fan section drives air along a bypass flow path of a turbo fan engine; a fan shaft driving said fan and said fan rotates about a central longitudinal axis of said turbofan engine; a speed reduction device including an epicyclic gear system; a turbine section connected to the fan section through the speed reduction device and said turbine section rotates about said central longitudinal axis; a first fan bearing for supporting rotation of the fan hub located axially forward of the speed reduction device; a second fan bearing for supporting rotation of the fan hub located axially aft of the speed reduction device; and a first outer race of the first fan bearing fixed relative to the fan hub, wherein the second fan bearing includes an outer race and the outer race of the first fan bearing and the outer race of the second fan bearing are fixed relative to the fan hub and rotate with the fan hub in the same direction.
 2. The gas turbine engine of claim 1, including an inner race of the first fan bearing fixed from rotation relative to an engine static structure and an inner race of the second fan bearing fixed from rotation relative to the engine static structure.
 3. The gas turbine engine of claim 2, wherein the epicyclic gear system includes a sun gear, star gears, a ring gear mechanically attached to the fan section, and a carrier, the carrier being fixed from rotation relative to the engine static structure.
 4. The gas turbine engine of claim 3, wherein the first fan bearing and the second fan bearing include at least one of roller bearings, ball bearings, or tapered bearings and each of the star gears include a star gear bearing.
 5. The gas turbine engine of claim 4, wherein the carrier includes multiple flexible posts for mounting each of the star gears and the star gear bearing.
 6. The gas turbine engine of claim 2, wherein the first fan bearing is at least partially axially aligned with a fan blade of the fan section.
 7. The gas turbine engine of claim 2, including a carrier fixed from rotation relative to an engine static structure without a static flexible mount.
 8. The gas turbine engine of claim 2, wherein an inner race of the first fan bearing is fixed from rotation relative to a carrier and the carrier is fixed from rotation relative to an engine static structure.
 9. The gas turbine engine of claim 2, including a rotating compartment wall configured to rotate with the compressor section and form a seal with an engine static structure.
 10. The gas turbine engine of claim 2, wherein the speed reduction device is located radially inward from a first compressor and the speed reduction device is axially aligned with the first compressor.
 11. A fan drive gear module comprising a sun gear; a multitude of intermediate gears surrounding the sun gear; a carrier supporting the multitude of intermediate gears, the carrier is configured to support a fan hub with a first fan bearing located on a first side of the carrier and a second fan bearing located on a second opposite side of the carrier, wherein the carrier is configured to be fixed from rotation relative to an engine static structure without a static flexible mount; and an outer race of the first fan bearing and an outer race of the second fan bearing are fixed relative to the fan hub and rotate with the fan hub in the same direction.
 12. The fan drive gear module of claim 11, wherein an inner race of the first fan bearing is fixed from rotation relative to a carrier and the carrier is fixed from rotation relative to the engine static structure.
 13. The fan drive gear module of claim 12, wherein each of the multitude of intermediate gears include an intermediate gear bearing and the carrier includes multiple flexible posts for mounting each of the multitude of intermediate gears and the intermediate gear bearing.
 14. The fan drive gear module of claim 11, including a ring gear fixed relative to the fan hub and the first fan bearing and the second fan bearing include at least one of roller bearings, ball bearings, or tapered bearings.
 15. A method of designing a gas turbine engine comprising: coupling a speed reduction device between a fan hub and a low pressure turbine drive shaft; positioning a first fan bearing axially forward of the speed reduction device, wherein an outer race of the first fan bearing is fixed relative to the fan hub and rotates with the fan hub relative to an engine static structure; and positioning a second fan bearing axially aft of the speed reduction device and an outer race of the second fan bearing is fixed relative to the fan hub and rotates in the same rotational direction and at the same rotational speed as the outer race of the first fan bearing.
 16. The method of claim 15, including positioning an inner race of the first fan bearing and an inner race of the second fan bearing fixed to a carrier and fixed from rotation relative to the engine static structure.
 17. The method of claim 15, including fixing a ring gear of the speed reduction device relative to the fan hub to allow the ring gear to rotate with the fan hub and the first fan bearing and the second fan bearing include at least one of roller bearings, ball bearings, or tapered bearings. 